Nature's GMOs: Parasites Alter Butterfly Genomes Using Viruses

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Genetically modified organisms may usually be thought of as human
creations, but scientists now find that monarch butterflies,
silkworms, and many other butterflies and moths naturally possess
genes from parasitic wasps. These genes were acquired through a
virus that weaves in and out of DNA, the researchers found.

Butterflies and moths may have kept these wasp
genes because they protect against other viruses, the
researchers added.

Along with those eggs, these wasps also inject
giant viruses, known as bracoviruses, which can incorporate
themselves into the genomes of the caterpillars, the researchers
said. Bracoviruses invaded wasps about 100 million years ago, and
now are created exclusively inside wasp ovaries from viral DNA
inside the genomes of the insects, the scientists added.

Bracoviruses help wasp larvae survive within their hosts. Once
the bracoviruses weave themselves into the genomes of the
caterpillars, the viruses can inhibit the immune defenses of
these caterpillars, protecting the wasp larvae.

However, caterpillars might sometimes repel braconid attacks, for
instance, by eliminating the eggs or killing the larvae.
Caterpillars may have an especially good chance of surviving
these braconid assaults if they get attacked
by wasps that do not normally parasitize their species. Since
they survive such attacks, this means caterpillars with genes
modified by bracoviruses could grow up into butterflies or moths
and pass these changes on to their offspring.

Now, scientists find that bracoviruses at times brought wasp
genes with them. These tag-along genes were found in the monarch
butterfly, the silkworm, and pests such as the
fall armyworm and the beet armyworm, the scientists said.

"I was so surprised, I couldn't believe it — I thought at the
beginning that there was a mistake somewhere," study co-senior
author Jean-Michel Drezen, a virologist at the University of
Tours in France and research director of France's National Center
for Scientific Research, told Live Science. "But we could verify
experimentally that it was true."

The wasp, bee and ant lineage diverged from the butterfly and
moth lineage about 300 million years ago, about the same time the
ancestors of mammals diverged from the
ancestors of reptiles. The differences between wasp genes
those of butterflies and moths were therefore significant enough
for the scientists to distinguish the two.

"Our results show that genetically modified insects are being
created by nature without the need of a laboratory," said study
co-senior author Salvador Herrero, a molecular biologist and
insect pathologist at the University of València in Spain.

The scientists discovered that some of these wasp genes help
protect caterpillars against baculoviruses, which are viruses
that farmers sometimes use to control insect pests. Specifically,
the researchers found that these "domesticated" genes may help
keep the viruses from moving around inside the insects.

Previous research has found that viruses can ferry genes between
species. Mutations often degrade these sequences of DNA over the
course of many generations, but if the genes benefit their hosts,
they can survive largely intact for millions of years, as the
wasp genes did in butterflies and moths.

Tens of thousands of braconid wasp species exist, and these
insects parasitize virtually all butterfly and moth species. This
suggests that naturally genetically
modified butterflies and moths are commonplace around the
world, the researchers said.

One potential implication of these findings is that if people
genetically modify insects, those genes could inadvertently make
their way into other species. For instance, genes artificially
introduced into parasitic wasps that are used to control pests
may accidentally get transferred into the genomes of the pests,
the researchers said.

"We must be aware of the type of genes that we add, since they
could be also transferred to other insects," Herrero told Live
Science.